Where bearing structures, such as pillow blocks, having either spherical or tapered roller bearings or ball bearings, are used for supporting rotatable shaft members, the inner race must be securely locked to the shaft for the bearing structure and associated machinery to operate properly and efficiently. If slippage occurs, the generated forces will be borne by the race instead of the balls or rollers in the bearings. Since lubrication is not supplied to the interface between the shaft and inner race, such slippage results in undesirable metal-to-metal sliding contact, with an associated heat buildup from the friction generated, fretting corrosion, wear, and eventual failure of some or all of the related elements. Many methods have been used to secure the inner race to the shaft. For example, the race may be shrunk or press-fitted to the shaft, which provides a relatively secure grip but requires extremely close tolerances, is generally more expensive than other methods, and makes removal of the fitted elements difficult. Another more common method involves the use of set screws threaded radially through the inner race to contact the shaft in an interface fit, or threaded radially through an over-collar and through an unthreaded hole in the inner race to contact the shaft. An additional method involves the use of a set screw threaded axially through a locking collar, to abut a tapered adapter sleeve and wedge the sleeve against the oppositely tapered outer surface of the inner race, combined with radially disposed set screws in an over-collar, as disclosed in U.S. Pat. No. 3,957,319, owned by the assignee of the present invention.
The use of set screws in any of the previously described embodiments has certain disadvantages. The inner race is normally hardened in the raceway area, with minimum resiliency to withstand the rotative and thrust forces applied by the roller or ball bearing elements. Thus, where set screws are threaded through the inner race, any vibration is transmitted directly to the set screws from the hardened race, leading to loosening of the screws and slippage of the race. The screws may also cause both axial and radial deflection of the inner race, which can extend into the raceway area. Such deflection in the raceway is undesirable, due to load concentration and distortion and adverse vibration in the bearing structure. Additionally, most radially disposed set screws, which are threaded through an over-collar into an unthreaded hole or gap formed in the inner race are easily loosened from vibration or other movements generated through operation of the machinery, and have a tendency to "work" against the inner race, thus causing further loosening and wear on the inner race.